In an Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiplexing Access (OFDM/OFDMA) system, a base station (BS), which supports a plurality of antennas, can attain transmission diversity gain by receiving feedback information from a mobile subscriber station (MSS). The feedback information includes weight value(s) or channel information. Here, the feedback information is transmitted from the MSS to the BS via an uplink transmission high speed (or fast) feedback channel.
In detail, the feedback information relates to various determined (or measured) information of the BS transmission signals. The feedback information provides necessary information for the BS to transmit more accurate transmission signals. Here, the determined information can include various determined value(s) of downlink transmission signals. For example, the determined value of the downlink signal can be a signal/noise (S/N) value or a weight or selected mode value (space-time transmit diversity or spatial multiplexing) in case of multi-input multi-output (MIMO).
FIG. 1 illustrates an example of a MSS sending to a BS feedback information, which includes weight values (or channel information), acquired in a downlink transmission. As illustrated in FIG. 1, the BS, which uses a plurality of antennas, informs the MSS of a space-time coding (STC) mode via a STC zone IE message. The STC mode is determined based on a number of antennas possessed by the BS. At the same time, the BS notifies the MSS which matrix type (e.g., type B) the BS plans to use. The multi-input multi-output (MIMO) downlink (DL) basic IE message is the avenue through which the BS notifies the MSS of which matrix type it plans to use. Furthermore, the BS notifies to the MSS via a Channel Quality Indicator Channel (CQICH) Enhanced Allocation IE message the mapping scheme of the weight value to be assigned to the uplink high speed feedback channel.
On the other hand, the MSS determines the downlink channel quality or acquires a weight matrix W based on the downlink channel quality determination. The size of the weight matrix is determined by the number of BS transmission antennas and the number of output signals according to the STC scheme. The following Equation 1 is an example of the weight matrix W in connection with four BS transmission antennas and two STC outputs.
                    W        =                  [                                                                      w                  11                                                                              w                  12                                                                                                      w                  21                                                                              w                  22                                                                                                      w                  31                                                                              w                  32                                                                                                      w                  41                                                                              w                  42                                                              ]                                    [                  Equation          ⁢                                          ⁢          1                ]            
The MSS sends feedback of the weight matrix W and the channel quality information acquired through Equation 1 via the CQICH (S12). In order to improve the signal-to-noise ratio (SNR) in the receiving end by the BS, which uses a plurality of transmission antennas, the BS receives a downlink determined value or a weight value. At the same time, the BS allocates the uplink CQICH to the MSS in order to receive the downlink determined value or weight value.
Additionally, in the existing 802.16 OFDMA system, a message of the fast feedback channel of the uplink is allocated to an uplink slot. Here, an uplink slot indicates one sub-channel zone, which encompasses three symbols, and is comprised of six tiles. A slot of IEEE 802.16 OFDMA system refers to the smallest unit available for data allocation and can be expressed in time domain and sub-channel domain. Moreover, a tile comprises eight data sub-carriers.
Table 1 provided below shows a method by which sub-carriers of a fast feedback channel are modulated. Moreover, Table 2 shows sub-carrier modulation method as applied to each vector of Table 1.
TABLE 1Vector indices to be used by4 bitfast feedback channel per tilepayload(tile 0, tile 1 . . . tile 5)0b00000, 0, 0, 0, 0, 00b00011, 1, 1, 1, 1, 10b00102, 2, 2, 2, 2, 20b00113, 3, 3, 3, 3, 30b01004, 4, 4, 4, 4, 40b01015, 5, 5, 5, 5, 50b01106, 6, 6, 6, 6, 60b01117, 7, 7, 7, 7, 70b10000, 1, 2, 3, 4, 50b10011, 2, 3, 4, 5, 60b10102, 3, 4, 5, 6, 70b10113, 4, 5, 6, 7, 00b11004, 5, 6, 7, 0, 10b11015, 6, 7, 0, 1, 20b11106, 7, 0, 1, 2, 30b11117, 0, 1, 2, 3, 4
TABLE 2Data sub-carrier modulationmethod per each vector indexVector(sub-carrier 0, sub-carrier 1 . . .Indexsub-carrier 7)0P0, P1, P2, P3, P0, P1, P2, P31P0, P3, P2, P1, P0, P3, P2, P12P0, P0, P1, P1, P2, P2, P3, P33P0, P0, P3, P3, P2, P2, P1, P14P0, P0, P0, P0, P0, P0, P0, P05P0, P2, P0, P2, P0, P2, P0, P26P0, P2, P0, P2, P2, P0, P2, P07P0, P2, P2, P0, P2, P0, P0, P2
As shown in Table 1 and Table 2, the feedback information is expressed as payload in four (4) bits, and based the payload value, vector indices of six (6) tiles to be used in the fast feedback channel can be attained. Furthermore, eight (8) sub-carriers are provided with different modulation values based on each vector index.                The following are equations regarding each modulation scheme (P0, P1, P2, P3) with respect to Table 2.        
            P      ⁢                          ⁢      0        =                  1                  2                    ·              exp        ⁡                  (                      j            ·                          π              4                                )                                P      ⁢                          ⁢      1        =                  1                  2                    ·              exp        ⁡                  (                      j            ·                                          3                ⁢                                                                  ⁢                π                            4                                )                                P      ⁢                          ⁢      2        =                  1                  2                    ·              exp        ⁡                  (                                    -              j                        ·                                          3                ⁢                π                            4                                )                                P      ⁢                          ⁢      3        =                  1                  2                    ·              exp        ⁡                  (                                    -              j                        ·                          π              4                                )                    
The MSS using a plurality of antennas has to receive feedback information from the BS in order to achieve transmission diversity. The feedback information includes the uplink determined value (channel information or weight value). However, there is not a defined channel which allows for fast feedback of the BS determined value to the MSS.